The invention relates to an open roof construction for a vehicle, having a roof opening which can be closed by a movable closure element, wherein the element is used for varying the light transmission through the roof opening.
In order to enhance the degree of comfort in a vehicle fitted with an open roof construction having a roof opening approaches are sought for varying the amount of incident light through the roof opening. Dutch patent application no. 9102116, from which the present invention departs, discloses an open roof construction wherein the closure element consists of a sliding panel, which is provided with a coating that exhibits variable light transmission. The variable light transmission proves to be advantageous when the panel closes the roof opening entirely or for the is greater part. However, when the panel is moved to a position in which it opens the roof opening, the coating exhibiting variable light transmission loses its function.
Another approach used in prior art open roof constructions is a sunscreen present under the closure element. In this case, light transmission through the roof opening can be varied by changing the position of the sunscreen to a greater or lesser degree so as to cover the roof opening to a greater or lesser degree. In fact, the designer opts for a principle whereby the extent of the shade provided by the sunscreen is varied. In principle, there is no regulation of light intensity.
In accordance with one aspect of the present invention, the open roof construction includes a sliding sunscreen positioned under the closure element, wherein the sunscreen at least partially has a material that exhibits variable light transmission. The roof opening can be covered by the sunscreen to a degree that can be freely selected. Consequently, it is possible in the selected position of the sunscreen to vary light transmission through a roof opening.
Within the scope of the invention the sunscreen may consist substantially entirely of a material that exhibits variable light transmission. The sunscreen may also have a central portion that exhibits variable light transmission and a frame that surrounds the central portion, wherein the frame consists of a material that does not exhibit variable light transmission.
In the latter case an advantageous embodiment may be one wherein the central portion can be detached from the surrounding frame. In this way it is possible to build a central portion into any conventional sunscreen prior to, during and after the fitting of the open roof construction in a vehicle.
The open roof construction according to the invention provides a number of advantages. The construction according to the present invention can be used with practically any conventional open roof construction. Since the movable closure element no longer has a coating or a portion that exhibits variable light transmission, as is the case with the prior art, the design restrictions with regard to the closure element are less stringent. Furthermore, possible damage to the light-transmitting material can be repaired more easily and at lower expense, since it is only necessary in the worst case to replace the sunscreen. Whereas, in the prior art, it would be necessary in the worst case to replace the entire closure element.
In spite of the fact that the sunscreen now consists, at least partially so, of a material that exhibits variable light transmission, the sunscreen can continue to perform other functions, such as acoustic and thermal insulation. This enables the sunscreen to provide the same degree of luxury as any other conventional sunscreen.
In another embodiment of the open roof construction according to the present invention, light transmission is varied automatically. This can for example be achieved when light transmission is varied on the basis of measured quantities inside the vehicle, such as light intensity or temperature, for example. For instance, if the temperature inside the vehicle rises or threatens to rise too high, the degree of light transmission can be reduced automatically, thus reducing the heating influence of the incident light.
It is also possible, of course, to vary the light transmission manually. In that case the driver or a passenger of the vehicle can select a degree of light transmission to his or her liking.
An electrochromatic material may be selected as a suitable material exhibiting variable light transmission. Components consisting of such electrochromatic material are known and can be used in accordance with widely varying specifications.
An inexpensive variant of the open roof construction according to the invention provides an embodiment wherein the material that exhibits variable light transmission consists of polarisation filters arranged in side-by-side relationship, which can be pivoted or otherwise moved with respect to each other. As is known, the amount of light penetrating through the polarisation filters can be regulated between a maximum value and a minimum value by pivoting the two filters relative to each other.